1. Field of the Invention
This invention relates to titanium trihalide solids products having a narrow particle size distribution and an average particle size diameter greater than about 25 microns and preferably greater than about 35 microns. The invention further relates to the method of producing large particle size titanium trihalide solids products and activating the solids products to an active form of titanium trihalide useful for the polymerization of alpha-olefins such as propylene to highly stereoregular polyolefins granules having a narrow particle size distribution and an average particle size greater than about 600 microns and preferably about 1,000 microns or greater.
2. Description of the Prior Art
Traditionally olefin polymers are used as a material for the manufacturing of injection molded articles such as transport cases, buckets, and the like, and blow molded articles such as bottles, cans and the like. In these molding processes the olefin polymer is generally employed in the form of pellets. In order to obtain polyolefin pellets a pellatizing step is necessary.
Because of the increasing cost of energy it would be highly desirable to eliminate the pelletizing step. However, the polyolefin obtained from the polymerization reactors have heretofore been generally in the form of a powder having a wide particle size distribution, poor pourability and undesirable amounts of polymer powder fines therefor discouraging its use in the powder form as material for molding processes.
It is highly desirable that the molding industry be provided with polyolefin polymers in the form of polymer granules having a narrow particle size distribution, a substantial absence of polymer fines and having an average particle size diameter of 600 microns or greater and preferably about 1,000 microns or greater. The provision of such polyolefin granules would generally eliminate the requirements for a pelletizing step thereby resulting in an economic advantage to the industry as well as to the ultimate consumer.
It is well known in the art that there is a parallel relationship between the morphology of the polymer as obtained from the polymerization reaction vessel and the morphology of the catalyst employed during the polymerization process, that is to say, the polymer produced tends to replicate the catalyst particle size, shape and morphology. Therefore, in order to obtain polymer granules having a narrow particle size distribution and average particle diameter of about greater than 600 microns and preferably about 1,000 microns or greater directly from the reaction vessel a titanium halide catalyst manifesting a narrow particle size distribution and an average particle size diameter of about 35 microns or greater and preferably about 45 microns or greater should be employed.
The prior art discloses several methods for obtaining large particle size Ziegler-type catalyst. For example, in U.S. Pat. No. 3,905,915 of Wristers, issued Sept. 16, 1975, there is disclosed a process for producing titanium trichloride catalyst by first obtaining a finely-divided preformed solid "seed" catalyst and thereafter sequentially reducing titanium tetrachloride in the presence of a reducing agent. In order to obtain large titanium halide particles it is recommended that 3 or more sequential reduction steps be performed. Additionally, the rate of reduction is controlled by slowly raising the temperature of the system at a controlled rate until the temperature of about 25.degree. C. is reached. The method results in the production of a layered catalyst particle due to the multiple reduction steps of titanium tetrachloride to titanium trichloride. Because of the layers, the catalyst particle as a whole is weak and easily broken into smaller particles under the preferred and normal chemical activation and polymerization conditions. The breakdown of the catalyst particle will result in the production of the undesirable polymer fines. Furthermore, polymer resins produced in the presence of the layered catalyst will readily disintegrate into smaller undesirable resin powders.
In U.S. Pat. No. 4,085,064 of Wristers, issued Apr. 18, 1978, there is disclosed a method for producing purple titanium trichloride with a molar excess of ethyl aluminum chloride and preferably ethyl aluminum dichloride. In Example 1, by controlling the rate at which temperature is raised during the production of the purple titanium trichloride there was obtained a catalyst having a wide particle size distribution of about 45 to 60 microns. The catalyst particles thus produced are more difficult to activate than the catalyst particle of this invention.
In U.S. Pat. No. 4,062,804 of Ueno et al, issued Sept. 13, 1977, and U.S. Pat. No. 4,127,504 and 4,127,505 of Ueno et al, each issued Nov. 28, 1978, the reduction of titanium tetrachloride in the presence of a mixture of diethylaluminum chloride and ethylaluminum dichloride to obtain the catalyst having a narrow particle size distribution is disclosed. The patent does not teach how to grow large size catalyst particles.
In British Pat. No. 1,393,430 of Van Der Bend, a method of preparing titanium trichloride catalyst particles having a narrow particle size distribution is disclosed. The process involves reduction of titanium tetrachloride by adding diethylaluminum monochloride to the titanium tetrachloride in the presence of particular amounts of monoethylaluminum dichloride. The growth of large size catalyst particles is not disclosed.
In Belgian Pat. No. 867054 there is disclosed a method of obtaining polymer particles having a narrow particle size distribution and reduced fines content. The improvement to the catalyst system consists in wetting the titanium trichloride with a mixture of alkanes and alkylbenzenes.
In U.S. Pat. No. 3,861,746 of Laffitte, issued June 24, 1975, there is disclosed a process for the production of hydrogen reduced titanium trichloride having an average particle size greater than 20 microns, preferably greater than 20 to 100 microns. The process for the production of the catalyst particle involves the crystallization of the titanium halide effluent from a reaction zone held at a temperature between 800.degree. C. and 1,200.degree. C.
In U.S. Pat. No. 4,077,903 of Wristers, issued Mar. 7, 1978 the reduction of titanium tetrachloride with a mixture of aluminum triethyl and aluminum diethyl chloride is accomplished at reduced temperatures and thereafter gradually elevating the temperature. Large particle size titanium trichloride was disclosed.
In U.S. Pat. No. 4,098,979 of Maemoto et al, issued July 4, 1978, there is disclosed a catalyst system comprising a catalyst component supported on a spheroidal particle of a high molecular weight carrier compound. The granule size distribution of the polymer obtained by polymerizing in the presence of the catalyst system is alleged to be controlled by controlling the particle size distribution of the carrier compound. Large size polyethylene granules are obtained by polymerizing in the presence of the catalyst system.
In U.S. Pat. No. 3,594,330 of Delbouille et al, there is disclosed the polymerization of alpha-olefins in the presence of a Ziegler-type catalyst deposited on a pulverulent support. The patentee teaches that when the support is in the form of microspheres the polymer is obtained by polymerizing in the presence of a catalyst in the form of small spheres.
It is apparent that it would be an advance in the state of the art to provide a simple method for the production of titanium halide catalyst particles which are substantially resistant to fracturing under normal activation and polymerization conditions, which evidence a narrow particle size distribution and large average particle size diameter, which process is simple and requires a minimum expenditure of energy.